A color filter is an essential constituent part for a liquid crystal display or a solid-state image pick-up device. The color filter is prepared using a curable composition containing a colorant (a pigment or a dye). In the case where the colorant is a pigment, it is necessary to add a dispersant to secure the dispersibility/dispersion stability. In particular, as a dispersant having excellent dispersibility/dispersion stability, a polymeric dispersant is being developed (see, for example, Japanese Patent Application Publication (JP-B) No. 63-30057 and Japanese Patent Application Laid-Open (JP-A) No. 9-169821). Such a polymeric dispersant is being used for a color filter of a liquid crystal display or the like (see, for example, Japanese Patent Application Laid-Open No. 9-176511 and Japanese Patent Application Laid-Open No. 2001-272524).
On the other hand, recently, in the liquid crystal displays, a higher image quality has been required as compared with conventional ones for a TV/monitor, and accordingly, improvements in contrast and color purity are required.
With respect to a curable composition for use in the production of a color filter, there is an attempt to improve the contrast by using a finer particle size of a pigment (see, for example, Japanese Patent Application Laid-Open No. 2006-30541).
However, if a pigment having a smaller particle size is used, there has been a problem that since the surface area of the pigment is increased, the dispersibility/storage stability is deteriorated. If the addition amount of a dispersant is increased to secure the dispersibility/storage stability, there occurs a problem that since the developability is reduced, it is hard to form a good pattern. On the other hand, if the addition amount of an alkali-soluble resin is increased to improve the developability, there occurs a problem that dispersibility/storage stability is deteriorated. That is, in the existing dispersants, it has been very difficult to simultaneously satisfy the dispersibility/storage stability/developability.
Furthermore, it has been recently essential to reduce a pixel size (reduction in the pattern width or the film thickness) in response to improvement of the pixel number in a solid-state image pick-up device. Accordingly, it is required to increase the pigment concentration in the curable composition. However, if the pigment concentration is increased, there occurs a problem that since the content of the dispersion resin/alkali-soluble resin in the curable composition should be reduced, the dispersibility/dispersion stability/developability are deteriorated, and as a result, it is difficult to form a pattern.
That is, recently, there have been difficulties in producing a color filter having good color characteristics with a high contrast corresponding to a high-performance solid-state image pick-up device/liquid crystal display using a curable composition containing a conventional dispersant, and there is a demand for a dispersant which can satisfy dispersibility/storage stability and developability simultaneously.